Below are a synopsis of some tips I got years ago from a friend who was a professional camera man. I'm not a professional but I found his advise useful.

Light the scene properly - avoid back lighting and strong overhead light that casts dark shadows, natural daylight through windows is best combined with indoor lighting that has a horizontal angle component. Set white balance on camera to suit candescent lighting, fluorescent lights, or sunshine if scene lit exclusively from windows on sunny day. Smartphones try and figure this out themselves.

Plan scenes - avoid birds eye view of model railway stock, best is side on or slightly elevated view

Avoid camera movement - use tripod or hold smartphone against solid object to avoid camera shake, or hold by hand as steady as possible.

Generally never zoom or pan a camera - allow the action to move through the scene.

If panning rotate camera very slowly and never back and forth

On rare occasions when zooming do so very slowly and only once per shot

If doing a tracking shot only the slightest horizontal tracking movement is needed to create the effect, avoid 'running' around a layout after a train. Use separate clips edited together.

Be ruthless when editing to cut unnecessary material and avoid repeat shots.

Sound - consider editing sound levels of recorded video if too loud

Sound - consider adding a backing music track that is not too loud, nor incompatible with the scenes depicted (e.g: meat loaf and sedately moving steam train are not really compatible). Soothing music that enhances rather than distracts from the viewing experience

Credits at start and end to summarise movie content is useful and allows a few seconds before movie starts

If relevant add the odd short caption during the movie for example to explain a scene location, etc, but avoid over doing it and keep text to a few short word.

When editing, cut, cut, cut - less is more if clips well edited together.